Saturday 25 April 2015

The Execution Unit, EU


The execution unit(EU):

The main function of EU is decoding and execution of the instructions. It tells the BIU that where to fetch instructions or data from.


Different Parts of Execution Unit(EU):-


                •ALU
                •Flag Register
                •General Purpose Registers
                •Pointer and Index registers

                •Decoder
                •Control Circuitry

Bus Interface Unit, BIU, Continue........


Instruction Pointer:-
      It is 16-bit register, which identifies the location of the next word of instruction code that is to be fetched in the current code segment.
      IP contains an offset instead of the actual address of the next instruction.
      The 20-bit address produced after addition of the offset stored in IP to segment base address in the CS is called the Physical address of the code byte.



The Queue:-
      The last section of BIU is the FIFO group of registers called a queue. It is basically a group of registers.
      This arrangement makes possible for the BIU to fetch the instruction byte while EU is decoding an instruction or executing an instruction which does not require use of buses.
      This arrangement is called pipelining.
      This is done to speed up the program execution.